uhhh, Anytime a config file is over written then whatever was the old config file is gone and the new config file is in effect. That said, can not hurt to look at each and make any wanted edits.
Chrome I have limited experience with. In firefox there is a procedure to export all ones preferences, bookmarks and such to a external medium, and import them back to the new install. I bet the same is doable in Chrome.
Unity observation: I installed 12.04 about a year ago (triple booting) and kept 10.04. After a bit of getting accustomed to the new interface and learning my way around, I find I prefer Unity and have not gone back to 10.04. Nor, have I replaced the unity desk top. Unity is different and takes a new outlook to find/accomplish tasks, but, once you know how - unity is faster and easier ! I did find that indepth documentation is lacking.
it's all a learning experience